Dual-Catalyst Technique Allows Better Control of Molecules

MADISON, Wis., April 24, 2014 — Chemical reactions usually happen on their own terms.

But now, researchers from the University of Wisconsin-Madison have discovered a way to create molecules with controlled chirality using sunlight as one of two catalysts.

“Chemists could never do [this] efficiently, and so the prejudice was that it was too difficult to do,” said Dr. Tehshik Yoon, a chemistry professor at the university and leader of the study.

Sunlight can power a chemical reaction via a new technique that controls chirality. Courtesy of University of Wisconsin-Madison.
Heat and UV light are common chemical reaction drivers, he noted. And while UV light can power reactions that heat cannot, it sometimes carries too much energy, making it unselective and creating unwanted byproducts.

The researchers began exploring ways to power chemical reaction with visible light via solar cell metals, including Ru(bpy)32+, that release electrons to produce electricity. Once this happened, a second catalyst was introduced to control chirality.

“We are taking the electrons that these metals spin out and using their energy to promote a chemical reaction,” Yoon said, comparing this to plants’ activity during photosynthesis.

Using a second catalyst, the researchers gained greater control and were able to hold the transforming chemicals in the correct orientation so the electrons could create only the desired chirality. The team soon discovered that by making a very slight change to the chiral control catalyst, a completely different product molecule shape was created.

“One reason this field has failed is that a single catalyst had to both absorb light and control the chirality,” Yoon said. “If you tweak the single catalyst, you change its effects. By separating the two roles, you can make all kinds of changes to chirality without messing up the photochemical catalyst.”

To date, the team’s experiments have resulted in square structures with four carbons that have proven difficult to make with heat or UV light.

The new technique could benefit material scientists, Yoon said, namely those in the pharmaceutical industry. He added that the researchers will continue exploring the creation of chemicals using UV light.

“These are part of an unexplored space in molecular diversity,” he said. “Now that we have a platform for using these catalysts in tandem, we are looking more broadly to see what else we can do.”